1. Field of the Invention
The present invention pertains to donor elements for thermal mass transfer, the use of such donor elements in an assemblage for imaging using a laser, and the manufacture of a color filter with those donor elements.
2. Description of Related Art
Thermal transfer donor elements can be used in assemblages of a donor element and a receiver element to transfer a layer of material from the donor element to the receiver element. Certain polyols having a plurality of hydroxyl groups have been disclosed as an ingredient in a thermal transfer donor element.
U.S. Pat. No. 6,228,543B1, “THERMAL TRANSFER WITH A PLASTICIZER-CONTAINING TRANSFER LAYER” by Mizuno et al. assigned to 3M Innovative Properties Company, and incorporated herein by reference, discloses that plasticizers can be used in a transfer layer of a transfer unit of a thermal transfer donor element. The transfer unit includes all of the layers that can be transferred from the thermal transfer element. The transfer unit can have a single layer or multiple layers. At least one of these layers is a plasticizer-containing layer. At least one plasticizer-containing layer is typically positioned within the thermal transfer element to form an exterior surface of the transfer unit so that the plasticizer-containing layer is brought into contact with the receiver element during transfer. The remainder of the layers of the transfer unit are typically positioned between the exterior plasticizer-containing layer and the substrate. Additional layers of the transfer unit can be formed using a variety of materials and configurations, including those described, for example, in U.S. Pat. Nos. 5,156,938; 5,171,650; 5,244,770; 5,256,506; 5,387,496; 5,501,938; 5,521,035; 5,593,808; 5,605,780; 5,612,165; 5,622,795; 5,685,939; 5,691,114; 5,693,446; and 5,710,097, all incorporated herein by reference.
The plasticizer-containing layer of the transfer unit includes at least a binder composition and a plasticizer. The addition of plasticizer can reduce the softening temperature and/or viscosity of the binder composition to facilitate the transfer of the transfer unit to the receptor. Alternatively or additionally, the addition of plasticizer can increase the interaction between the binder composition and the receptor surface so that the binder composition adheres better to the receptor surface.
The binder composition and plasticizer are selected so that, after transfer, the binder composition and plasticizer of the transferred portion of the transfer unit can be co-reacted to bind the plasticizer in the imaged transfer layer. The plasticizer is bound within the imaged transfer layer to prevent or reduce the diffusion of the plasticizer to adjacent layers, devices, elements, or components of an article that includes the imaged transfer layer. In at least some applications, diffusion of the plasticizer out of the imaged transfer layer can harm, damage, or destroy the function of other layers, devices, elements, or components of the article. The plasticizer is bound to the binder composition by, for example, copolymerization or cross-linking of the plasticizer and at least one component of the binder composition.
For example, a thermal transfer element with a plasticizer-containing layer can be used in the formation of an electronic display (e.g., an LCD display). The thermal transfer element could be used to form at least a portion of a component of the display, such as, for example, a color filter, a black matrix, and/or spacers. In this application, the presence of substantial amounts of unbound plasticizer in a thermally imaged transfer layer might harm or damage the function of other portions of the display by, for example, diffusion of the plasticizer. In this instance, binding a substantial portion of the plasticizer with the binder composition of the transferred plasticizer-containing layer can reduce or prevent this harm or damage.
A single plasticizer or a combination of plasticizers can be used. The plasticizer can be a monomeric, oligomeric, or polymeric compound. Suitable plasticizers include compounds that reduce the softening point of the binder composition and have reactive functional groups to bind with the binder composition. Reactive functional groups include, for example, epoxide, carboxylic acid, hydroxyl, ethylenic-unsaturated (e.g., olefinic), vinyl, acrylic, methacrylic, amino, ester, mercapto, labile halo, imino, carbonyl, sulfonic acid, and sulfonic ester functional groups and any functional group that is capable of participating in a Diels-Alder reaction. Examples of suitable plasticizers include epoxides, phosphates (such as, for example, (meth)acryloyloxyalkyl phosphates), polyoxyethylene aryl ethers, esters, glycols and glycol derivatives, glycerol and glycerol derivatives, terpenes and terpene derivatives, and halogenated hydrocarbon compounds having reactive functional groups.
A donor element for use in a laser-induced thermal imaging process is disclosed in WO2003099574 A1 “LOW MOLECULAR WEIGHT ACRYLIC COPOLYMER LATEXES FOR DONOR ELEMENTS IN THE THERMAL PRINTING OF COLOR FILTERS”, of Jon Caspar et alia, incorporated herein by reference. The donor element includes a support layer; a heating layer; and a colorant containing thermally imagable layer comprising a crosslinkable binder having a number average molecular weight of about 1,500 to about 70,000. Some suitable pairs of functional groups for the crosslinking reactions include: hydroxyl and isocyanate; hydroxyl and carboxyl; hydroxyl and melamine-formaldehyde; carboxyl and melamine-formaldehyde; carboxyl and amine; carboxyl and epoxy, epoxy and amine; and carboxylic anhydride and amine. The epoxy/carboxyl and melamine-formaldehyde/carboxyl pairs are particularly effective since common aqueous pigment dispersants contain carboxyl groups which also can be incorporated into the final crosslinked polymer matrix. The pairs of crosslinking functional groups can be utilized in several ways. One crosslinking functional group can be incorporated into the binder polymer backbone, and the other added as a polyfunctional low molecular weight crosslinking agent. One crosslinking functional group can be incorporated into the binder polymer backbone, and the other incorporated into a different binder polymer backbone. Both of the crosslinking functional groups can be incorporated into the same binder polymer backbone. The desired crosslink density of the final color filter dictates relative amounts of the pairs of crosslinking monomers.
U.S. Pat. No. 5,691,098, “LASER-INDUCED MASS TRANSFER IMAGING MATERIALS UTILIZING DIAZO COMPOUNDS” by Busman, et al. assigned to Minnesota Mining and Manufacturing Company, and incorporated herein by reference, it is disclosed that thermal mass transfer materials are materials that can be removed from a substrate or donor element by the process of absorption of intense electromagnetic radiation. Depending on the intensity of the laser-light, light to heat conversion within or adjacent the materials can cause a melting of materials and/or gas production within or adjacent to them. Gas production may be the result of evaporation, sublimation, or thermal decomposition to gaseous products. Expansion of the gas may cause delamination from the donor substrate or propulsion of materials from the donor to a receptor. The latter process is often termed ablation. Melting or softening of the material promotes adhesion to the receptor. The overall transfer process thus involves ablative or melt-stick transfer or a combination of the two.
In some applications it is desirable to transfer curable materials such as crosslinkable resins. In those applications the thermal mass transfer material may be an oligomer. Suitable polymerizable materials include acrylate- or epoxy-terminated polysiloxanes, polyurethanes, polyethers, epoxides, etc. Suitable thermal crosslinkable resins include isocyanates, melamine formaldehyde resins, etc. Polymerizable and/or crosslinkable, transferable binders are particularly valuable for the manufacture of filter arrays for liquid crystal devices, in which the color layer must resist several subsequent aggressive treatment steps.
Any of the layers of the donor element can include an organic polymeric binder, including a wide variety of thermoplastic resins, thermosetting resins, waxes, and rubbers. They may be homopolymers and copolymers. Multiple materials may be present simultaneously as compatible blends, phase separated systems, interpenetrating networks, and the like. Typically, these binders should be soluble or dispersible in organic solvents to aid in processing. Nonlimiting examples of such binders include olefinic resins, acrylic resins, styrenic resins, vinyl resins (including vinyl acetate, vinyl chloride, and vinylidine chloride copolymers), polyamide resins, polyimide resins, polyester resins, olefin resins, allyl resins, urea resins, phenolic resins (such as novolac and resole resins), melamine resins, polycarbonate resins, polyketal resins, polyacetal resins, polyether resins, polyphenylene oxide resins, polyphenylene sulfide resins, polysulfone resins, polyurethane resins, fluorine-containing resins, cellulosic resins, silicone resins, epoxy resins, ionomer resins, rosin derivatives, natural (animal, vegetable, and mineral) and synthetic waxes, natural and synthetic rubbers (e.g., isoprene rubber, styrene/butadiene rubber, butadiene rubber, acrylonitrile/butadiene rubber, butyl rubber, chloroprene rubber, acrylic rubber, chlorosulfonated polyethylene rubber, hydrin rubber, urethane rubber, etc). Water dispersable resins or polymeric latexes or emulsions may be used.
U.S. Pat. No. 6,242,152, “THERMAL TRANSFER OF CROSSLINKED MATERIALS FROM A DONOR TO A RECEPTOR” by John Staral et al. assigned to 3M Innovative Properties, and incorporated herein by reference, provides a thermal transfer donor element that includes a transfer layer comprising a fully or partially crosslinked material. The crosslinked transfer layer can be imagewise transferred from the donor element to a proximate receptor by imaging the donor element with radiation that can be absorbed and converted into heat by a laser-light-to-heat converter included in the donor element. The heat generated during imaging is sufficient to effect transfer of the crosslinked transfer layer.
Donor elements may be constructed of a substrate, a transfer layer that includes a crosslinked or partially crosslinked organic, inorganic, organometallic or polymeric material, and a laser-light-to-heat converter material. The transfer layer can include fully or partially crosslinked organic, inorganic, organometallic, or polymeric materials. Examples of suitable materials include those which can be crosslinked by exposure to heat or radiation, and/or by the addition of an appropriate chemical curative (e.g., H 2 O, O 2, etc.). Radiation curable materials are especially preferred. Suitable materials include those listed in the Encyclopedia of Polymer Science and Engineering, Vol. 4, pp. 350-390 and 418-449 (John Wiley & Sons, 1986), and Vol. 11, pp. 186-212 (John Wiley & Sons, 1988).
U.S. Patent Application 20020187418A1, “MULTICOLOR IMAGE-FORMING MATERIAL” by Nakamura et al. assigned to FUJI PHOTO FILM CO. LTD., and incorporated herein by reference, discloses thermal transfer sheets each comprising a support layer, a photothermal converting layer and an image-forming layer, wherein an image is formed by the method comprising the steps of: superposing each one of the at least four thermal transfer sheets on an image-receiving sheet to be in a state of the image-forming layer being in contact with the image-receiving layer; and irradiating the thermal transfer sheet with a laser beam to transfer an image in an area of the image-forming layer subjected to irradiation onto the image-receiving layer. The image-forming layer can contain a rosin-based resin, for example an esterified product of a rosin containing 30 mass % or more of an abietic acid type rhodinic acid and at least one kind of polyhydric alcohol selected from ethylene glycol, glycerol and pentaerythritol.
The image-forming layer in the thermal transfer sheet can contain a rosin-based resin having a softening point of 100° C. or less measured by a ring and ball method, preferably from 80 to 90° C., and an acid value of from 2 to 220, preferably from 11 to 180, and more preferably from 160 to 180. A softening point measured by ring and ball method can be measured according to JIS K2207, K7234. By adding the rosin-based resin having the above physical properties to the image-forming layer, the rosin-based resin functions as an excellent adhesive agent, and so the image formed on the image-forming layer in the thermal transfer sheet can be easily transferred to the image-receiving sheet with good definition. When the melting point of the rosin-based resin exceeds 100° C., the melting point of the image-forming layer itself increases, which results in the reduction of sensitivity, the deterioration of transfer to an actual paper, and the above effect cannot be exhibited. Further, when the acid value is less than 11, the transfer to an actual paper is deteriorated and also the above effect cannot be exhibited. For the rosin-based resin, a rosin, a hydrogenated rosin, a modified rosin, derivatives of these rosins (esterified products), and a rosin-modified maleic acid resin can be exemplified. For the rhodinic acid constituting the rosin-based resin, either an abietic acid type or a pimaric acid type can be used. Resins containing 30 mass % or more of an abietic acid type rhodinic acid are preferably used, and a rosin containing 30 mass % or more of an abietic acid type rhodinic acid, and the esterified products of the rosin and at least one kind of polyhydric alcohol selected from ethylene glycol, glycerol and pentaerythritol are more preferably used. The specific examples of the abietic acid type rhodinic acids include an abietic acid, a neoabietic acid, a palustric acid, a dihydroabietic acid, and a dehydroabietic acid. The rosin-based resin is preferably added to the image-forming layer in an amount of from 5 to 40 mass %, more preferably from 10 to 20 mass %. Styrene-maleic acid copolymer resins may be used in combination with the rosin-based resin in the above range of use amount.
U.S. Pat. No. 6,190,827 B1 by Charles Weidner assigned to Eastman Kodak, and incorporated herein by reference, discloses hydrogenated and partially hydrogenated rosin esters and similar rosin derivatives suitable in a colorant transfer layer. Commercially-available materials include the glycerol ester of partially hydrogenated wood rosin, such as Staybelite® Ester 10 (Hercules Inc.), the glycerol ester of hydrogenated rosin, such as Foral® 85 (Hercules Inc.) and the pentaerythritol ester of modified rosin, such as Pentalyn® 344 (Hercules Inc.).
U.S. Pat. No. 6,221,543, “PROCESS FOR MAKING ACTIVE SUBSTRATES FOR COLOR DISPLAYS” by Guehler et al. assigned to 3M Innovative Properties, and incorporated herein by reference, discloses that after selectively thermally transferring two or more color filter materials from donor elements, the color filters disposed on the active substrate can optionally be inspected for defects, alignment, and so forth. After an optional inspection, the color filters can be crosslinked, for example, by radiation curing, thermal curing, or exposure to chemical curatives. Crosslinking hardens the color filter material on the substrate, thereby making the color filters more chemically, physically, and/or thermally stable, and thus less susceptible to damage that can be caused by later processing or operation. An exemplary transfer layer composition for colorant transfer comprises 5-80% by weight colorant, 15-95% by weight resin, and 0-80% by weight crosslinking agent, dispersing agents, and additives. In one embodiment, color filter formulations suitable for use with through hole etching processes include those that have a colorant dispersed in a binder that is soluble in solvents compatible with active matrix display substrates. Examples include color filter materials that have a colorant dispersed in an alkali soluble resin and a water soluble thermal crosslinker. The alkali soluble resin can include an acrylic copolymer that contains an acrylic acid unit or a methacrylic acid unit, and the crosslinker can include a water soluble melamine resin.
An exemplary method for providing uniform spacers in flat panel displays is disclosed in U.S. Pat. No. 5,710,097. Spacer elements can be placed between substrates by selectively irradiating a thermal transfer donor sheet that comprises (a) a support, (b) an optional light-to-heat conversion layer, (c) an optional non-transferable interlayer, (d) a transferable spacer layer and (e) an optional adhesive layer. The process includes the following steps: (i) placing in intimate contact a receptor and the thermal transfer donor sheet described above, (ii) irradiating at least one of the thermal transfer donor sheet or the receptor (or a portion thereof, i.e., substrate, spacer layer, interlayer, light-to-heat conversion layer, and/or adhesive layer) with imaging radiation to provide sufficient heat in the irradiated areas to transfer the spacer layer to the receptor, and (iii) transferring the transferable spacer layer in the irradiated areas to the receptor. When the transferable spacer layer includes a thermosettable binder, the thermosettable binder may be crosslinked after transfer to the receptor. The binder may be crosslinked by any method which is appropriate for that particular thermosettable binder, for example, exposing the thermosettable binder to heat, irradiating with a suitable radiation source, or a chemical curative.
U.S. Pat. No. 6,682,862, “Method of fabricating color filter substrate for liquid crystal display device” by Chang et al. assigned to LG. Philips LCD Co., Ltd., and incorporated herein by reference, discloses a method of fabricating a color filter substrate for a liquid crystal display device that includes the steps of forming a black matrix on a substrate; adhering a color donor element to the substrate; disposing a laser head over the color donor element; repeatedly scanning the color donor element; and removing the color donor element so that a color filter pattern remains in color filter pattern regions defined inside the black matrix. End lines for each one of the repeated scans are located on the black matrix.
U.S. Pat. No. 6,866,979 by J. C. Chang et alia assigned to 3M Innovative Properties Company, and incorporated herein by reference, discloses a thermal transfer donor element which comprises a support, a light-to-heat conversion layer, an interlayer, and a thermal transfer layer. When the above donor element is brought into contact with a receptor and imagewise irradiated, an image is obtained which is free from contamination by the light-to-heat conversion layer. The construction and process of this invention is useful in making colored images including applications such as color proofs and color filter elements. Example 5 demonstrates the preparation and use of a thermal transfer donor with a thermoset interlayer and a crosslinkable transfer layer. The colorant transfer layer was a 15 weight % nonvolatiles content aqueous dispersion prepared by Penn Color, Doylestown, Pa., and consisted of Pigment Green 7 and Elvacite 2776 (ICI Acrylics, Inc., Wilmington, Del.) neutralized with dimethylethanolamine at a 3:2 pigment/binder ratio, containing 4 weight % Primid XL-552 (EMS American Grilon, Sumter, S.C.) relative to the polymer, and 1 weight % Triton X-100 relative to the total nonvolatiles content. Primid XL-552 is N,N,N′,N′-tetrakis (2-hydroxyethyl)-hexanediamide, having 4 hydroxyl groups per molecule.